Biology subjects

Hirashima, M.

Publications and source records attributed to Hirashima, M..

7 recordsLinked to original sources

bioRxiv2026

Action Progress Organizes Motor Memory

Many everyday actions, such as handwriting, can be performed fluently across a wide range of scales and speeds. This flexibility suggests that motor behavior relies on abstract representations that transcend low-level motor or sensory variables. However, how such abstract representations are formed from individual movement experiences remains unclear. Here, we test the hypothesis that motor memory is organized not only by physical state variables, but also by an abstract coordinate of action progress: the normalized progression of an intended action from initiation to completion. Using a series of motor adaptation experiments that dissociate action progress from kinematic variables and absolute time, we show that learned outputs are retrieved according to their position within an action. This progress-based coordinate spans the unfolding course of a planned action, whether a single reach or an action sequence, and operates continuously rather than as a simple early-late distinction. Together, these findings identify action progress as an abstract organizing coordinate through which the motor system may encode movement experiences as abstract motor memories, offering a framework for understanding the flexible generalization of human motor behavior.

neuroscience↗

bioRxiv2023

Decision uncertainty as a context for motor memory

The current view of perceptual decision-making suggests that once the decision is made, a single motor program associated with the decision is carried out, irrespective of the degree of uncertainty involved in the decision-making process. As opposed to this view, we show that different levels of decision uncertainty contextualize actions differently, allowing the brain to form different motor memories based on each context. The match between decision uncertainty during learning and retrieval is critical for successful motor memory retrieval. The same movement trajectory can be associated with different motor memories if each memory is linked to a different level of decision uncertainty. Encoding motor memories based on decision contexts may enhance the robustness of control during the varying neural activities induced by different cognitive states.

neuroscience↗

bioRxiv2021

Validity of freehand three-dimensional ultrasound system in measurement of three-dimensional surface shape of shoulder muscles

Freehand three-dimensional ultrasound (3DUS) system is a promising technique for accurately assessing muscle morphology. However, its accuracy has been validated mainly in terms of volume by examining lower limb muscles. This study aimed to validate 3DUS in the measurements of 3D surface shape and volume by comparing them with MRI measurements while ensuring the reproducibility of participant posture by focusing on the shoulder muscles. The supraspinatus, infraspinatus, and posterior deltoid muscles of 10 healthy males were scanned using 3DUS and MRI while secured by an immobilization support customized for each participant. A 3D surface model of each muscle was created from the 3DUS and MRI methods, and the agreement between them was assessed. For the muscle volume, the mean difference between the two models was within -0.51 cm3. For the 3D surface shape, the distances between the closest points of the two models and Dice similarity coefficient were calculated. The results showed that the median surface distance was less than 1.21 mm and Dice similarity coefficient was larger than 0.85. These results suggest that, given the above error is permitted, 3DUS can be used as an alternative to MRI in measuring volume and surface shape, even for the shoulder muscles.

bioengineering↗

bioRxiv2021

Neural network models for spinal implementation of muscle synergies

Muscle synergies have been proposed as functional modules to simplify the complexity of body motor control; however, their neural implementation is still unclear. Converging evidence suggests that output projections of the spinal premotor interneurons (PreM-INs) underlie the formation of muscle synergies, but they exhibit a substantial variation across neurons and exclude standard models assuming a small number of unitary "modules" in the spinal cord. Here we compared neural network models for muscle synergies to seek a biologically plausible model that reconciles previous clinical and electrophysiological findings. We examined three neural network models: one with random connections (non-synergy model), one with a small number of spinal synergies (simple synergy model), and one with a large number of spinal neurons representing muscle synergies with a certain variation (population synergy model). We found that the simple and population synergy models emulate the robustness of muscle synergies against cortical stroke observed in human stroke patients. Furthermore, the size of the spinal variation of the population synergy matched well with the variation in spinal PreM-INs recorded in monkeys. These results suggest that a spinal population with moderate variation is a biologically plausible model for the neural implementation of muscle synergies.

neuroscience↗

bioRxiv2021

Transcranial magnetic stimulation of the occipital cortex interferes with foot movements in blind individuals

Research has shown that the occipital cortex can be reorganized and repurposed for nonvisual perception and cognitive functions following visual loss in blind individuals. However, no studies have directly examined the involvement of the visual cortex in motor function. Here, we show that a rhythmic foot movement performed by acquired blind individuals can be disrupted by transcranial magnetic stimulation (TMS) to their primary and secondary visual cortex (V1/V2). This disruptive effect was absent for congenitally blind or sighted individuals. As a control, TMS to the neck muscles of acquired blind individuals confirms that this disruptive effect was not caused solely by the sensory (tactile/auditory) sensations accompanying the stimulation. Our results provide the direct evidence that functional repurposing of the human visual cortex is not restricted to perception and cognitive functions but also extends to motor function. Moreover, our findings suggest the nessecity of the visual experience before visual loss for the functional reorganization of the visual cortex for motor function. Significance statementThe brain can adapt remarkably after sensory loss. One striking example is that after visual loss, the visual cortex--deprived of visual input--is often reused for nonvisual perception and higher cognition. Here, we show that it can also support motor control. Using transcranial magnetic stimulation, we transiently disrupted processing in the visual cortex while participants performed rhythmic foot movements. This disruption impaired performance in people who became blind after birth, but not in sighted individuals or those blind from birth. These findings demonstrate that the visual cortex can take on a motor function after vision is lost, but only with prior visual experience.

neuroscience↗

bioRxiv2021

Hypoxia induced carbonic anhydrase mediated dorsal horn sensory neuron activation and induction ofneuropathic pain

Neuropathic pain such as that seen in diabetes mellitus, results in part from central sensitisation in the spinal cord dorsal horn. However, the mechanisms responsible for such sensitisation remain unclear. There is evidence that disturbances in the integrity of the spinal vascular network can be a causative factor in the development of neuropathic pain. Here we show that reduced blood flow and vascularity of the dorsal horn leads to the onset of neuropathic pain. Using rodent models (type 1 diabetes and an inducible endothelial specific vascular endothelial growth factor receptor 2 knockout mouse) that result in degeneration of the endothelium in the dorsal horn we show that spinal cord vasculopathy results in nociceptive behavioural hypersensitivity. This also results in increased hypoxia in dorsal horn sensory neurons, depicted by increased expression of hypoxia markers hypoxia inducible factor 1, glucose transporter 3 and carbonic anhydrase 7. Furthermore, inducing hypoxia via intrathecal delivery of dimethyloxalylglycine leads to the activation of dorsal horn sensory neurons as well as mechanical and thermal hypersensitivity. This shows that hypoxic signalling induced by reduced vascularity results in increased hypersensitivity and pain. Inhibition of carbonic anhydrase activity, through intraperitoneal injection of acetazolamide, inhibited hypoxia induced pain behaviours. This investigation demonstrates that induction of a hypoxic microenvironment in the dorsal horn, as occurs in diabetes, is an integral process by which sensory neurons are activated to initiate neuropathic pain states. This leads to the conjecture that reversing hypoxia by improving spinal cord microvascular blood flow could reverse or prevent neuropathic pain.

neuroscience↗

bioRxiv2019

Intracellular Galectin-9 controls dendritic cell function by maintaining plasma membrane rigidity

Extracellular Galectins constitute a novel mechanism of membrane protein organisation at the cell surface. Although Galectins are also highly expressed intracellularly, their cytosolic functions are poorly understood. Here, we investigated the role of Galectin-9 in dendritic cell (DC) surface organisation and function. By combining functional, super-resolution and atomic force microscopy experiments to analyse membrane stiffness, we identified intracellular Galectin-9 to be indispensable for plasma membrane integrity and structure in DCs. Galectin-9 knockdown studies revealed intracellular Galectin-9 to directly control cortical membrane structure via modulating Rac1 activity, providing the underlying mechanism of Galectin-9-dependent actin cytoskeleton organisation. Consequent to its role in maintaining plasma membrane structure, phagocytosis studies revealed that Galectin-9 was essential for C-type lectin receptor-mediated pathogen uptake by human DCs. This was confirmed by the impaired phagocytic capacity of Galectin-9-null murine DCs. Together, this study demonstrates a novel role for intracellular Galectin-9 in modulating DC function, which may be evolutionary conserved.

cell biology↗